Field of the Disclosure
Exemplary embodiments of the present disclosure relate to an expansion module for a PLC (Programmable logic Controller). Particularly, the exemplary embodiments of the present disclosure relate to the PLC expansion module sequentially connected to a basic unit configured to transmit/receive massive data at a high speed using USB (Universal Serial Bus) communication.
Discussion of the Related Art
PLCs (Programmable Logic Controller), which are widely used in industrial fields, may be divided into a small size PLC and a medium/large size PLC, by size of the number of input/output control points thereof.
The medium/large size PLC is characterized in that it has numerous expansion modules at a slow data processing speed, because the medium/large size PLC communicates in a bus interface method by installing a module at a base. The small size PLC generally uses a serial interface method through a connector, does not use the base method.
FIG. 1 is an exemplary block diagram illustrating a conventional PLC using serial connection. A number of expansion modules having various functions such as communication and input/output may be sequentially connected to a programmable basic unit.
Here, the basic unit exchanges required data with each of the expansion modules through a serial interface.
The basic unit and each of the expansion modules are connected through signal lines such as transmission (Tx), reception (Rx), Trigger, VCC (IC power-supply pin), and GND (Ground).
Each of the expansion modules receives a Trigger signal in consecutive order, and the basic unit proceeds with an initialization process to sequentially allocate an exchange number to each of the expansion modules.
Each of the expansion modules renders its Tx line in a high impedance state and is on standby during the initialization process. The expansion module responses to the basic unit by opening the Tx line, only when receiving a Trigger signal.
After completing the response to the basic unit, the expansion modules renders the Tx line back to the high impedance state and transmits a Trigger signal to an expansion module in a next terminal.
When such initialization process is completed, each of the expansion modules is allocated with its own exchange number. Afterwards, the basic unit transmits communication data with exchange number information through a Tx line of the basic unit, when the basic unit tries to interface with each of the expansion modules.
Each of the expansion modules receives communication data through a Rx line while being always on standby, and only an expansion module corresponding to exchange number of the relevant data transmits a response data. When the transmission is completed, the Tx line is rendered in a high impedance state for other expansion modules to use.
However, the speed of such conventional interface method is not high. Therefore, there occur problems that scan time of the PLC basic unit is increased and a lot of interface time is consumed when one or more expansion modules requiring massive data process at high speed are installed. Thus, the conventional interface method is hard to apply to the system requiring a high speed control.